The grain cleaner is a very important part of a combine harvester and is located inside the harvester vehicle. Various grain cleaner designs are known. Typically a grain cleaner includes an upper section in which a fan blows straw onto a series of adjacent straw walkers. The grains pass onto the upper of (typically) two or more sieves, the motion of which together with the settings of position-adjustable fingers of the sieves cleans the grains of various valueless components such as husks and dust.
Often two or three sieves are provided, one beneath the other to give rise to a sequential sieving process. The fingers of the lower sieve of a pair for this reason usually are set closer together than the fingers of the upper sieve. As a result the upper sieve removes coarse contaminants that then are not able to clog the fingers of the finer sieve below.
The straw walkers move straw separated from the remainder of the crop towards the rear of the combine harvester for ejection from the rear of the combine harvester as it moves in a field.
A further fan blows husks, dust, and other lightweight particles away from the cleaned grains.
The grains that are processed in the sieve(s) eventually fall through the lower sieve onto a clean grain sheet that causes them to move into an auger case. The auger continuously moves the grain towards a grain elevator which transports the grain into a graintank. There, an unloading tube conveys the grains into a wagon towed behind a tractor that moves alongside the combine harvester for this purpose.
FIG. 1 illustrates, in a simplified form, part of the inner construction of a conventional combine harvester 10.
In FIG. 1 crop plant parts ingested at the front of the forwardly moving combine harvester 10 are threshed in a threshing section 11 where the action of a threshing drum 12a and separator 12b separates grains from stalks.
The stalks generally convey onto a series of adjacent, elongate straw walkers 13 as explained above by means of which they are conveyed towards the rear of the combine harvester 10 for cutting to consistent length and egestion onto the ground behind the combine harvester (or baling) 10. The threshed crop falls from concaves 14 of the threshing section 11 onto a grain pan 16 and thence is moved onto a series of sieves 17, 18, and 19 described in more detail below. The sieves 17-19 serve to clean the grain and prepare it for storage in a grain tank of the combine harvester 10.
The sieves in the example illustrated in FIG. 1 include a pre-sieve 17, an upper sieve 18, and a lower sieve 19 and are desirable because the action of the threshing section 11 does not remove all the valueless plant parts, such as husks, from the grains, and also because a certain percentage of the ears fed through the threshing section are incompletely threshed.
The operation of the sieves 17-19 is described below. Broadly speaking grains that are separated from stalks in the threshing section 11 fall through the concaves 14 onto grain pan 16 that reciprocates to move them onto the sieves 17, 18 and 19 in sequence.
Grains that are free of unusable material such as husks and other plant parts are small enough to fall through the lower sieve 19 onto a clean grain pan or sheet 21 located beneath the lower sieve 19. From the clean grain sheet 21 such grains pass into an auger case of the combine harvester 10. A clean grain auger represented by numeral 22 continuously evacuates the clean grain towards a grain elevator that transports the grain into the graintank of the combine 10.
As mentioned, not all the harvested grains are completely threshed and cleaned by the threshing and sieving parts 11, 17-19 of the combine harvester 10, however. Such incompletely threshed grains fall from a rear end 19a of the lower sieve 19 or, if the incompletely threshed grains are too large to pass through the upper sieve 18, from a rear end 18a of upper sieve 18, onto a tailings sheet or return grain sheet 23.
The tailings sheet 23 is similar to the clean grain sheet 21 with the exception that it conveys incompletely threshed grains to a re-threshing area 24a, instead of clean the clean grain auger 22.
The pre-sieve 17, upper sieve 18, and lower sieve 19 include upwardly pointing fingers that define a mesh of spaces. The positions of the fingers of at least the upper sieve 18 and the lower sieve 19 are adjustable such that the fineness of each sieve may be set. Under almost all circumstances the upper sieve 18 is arranged to sieve more finely than the pre-sieve 17 and less finely than the lower sieve 19. As grains move from the pre-sieve 17 to the upper sieve 18 and then to the lower sieve 19 therefore a progressively less coarse sieving action takes place until clean grains of sufficiently small size pass through the mesh defined by the lower, and hence least coarse, sieve 19.
A fan 26 is positioned forwardly of the sieves 17, 18, 19 and blows away unwanted matter such as dust, husks and plant parts that are discriminated by and therefore accumulate on the sieves 17-19 during their operation. Careful control of the sieve settings and the speed of the fan 26 results in the aforementioned effect of grains falling onto the clean grain sheet 21 and incompletely threshed crop falling onto the tailings sheet 23.
The grain pan 16, pre-sieve 17, upper sieve 18, lower sieve 19, clean grain sheet 21, and tailings sheet 23 in the conventional combine harvester 10 of FIG. 1 are all powered to move in order to move grain from one part of the machine 10 to another and to effect a cleaning action. The motions of the aforementioned components are best described with reference to FIG. 2, which shows the manner in which they are interconnected.
With reference to FIG. 2, a first rigid link 28 is secured at one end by an eccentric drive to a motor or rotary drive shaft 27 and at its opposite end via a pivot 31 to a so-called upper shoe 29 to which the pre-sieve 17 and the upper sieve 18 are rigidly mounted. The upper shoe 29 is constrained to move at an angle determined by neutral position of the upper parts of links 42 and 39 (described below) as judged with reference to FIG. 2. Rotation of the motor or drive shaft 27 causes repeated reciprocating back and forth movement of the upper shoe 29.
At the forwardmost end of upper shoe 29, a cranked, rigid link 32 is secured by way of a further pivot 33, and at its end remote from the upper shoe 29 is pivotably secured to a further rigid link 34 that at its opposite end is secured by way of another pivot 36 to the underside of the grain pan 16. Further, rigid link 34 is constrained by a pivoting yoke 37 approximately mid-way along its length; and a pivoting support link 38 supports the rear end of the grain pan 16. In some other conventional designs the upper shoe 29 and grain pan 16 move in the same direction and with the same motion, as a result of the pivot 33 being directly connected to the grain pan 16.
As a result of the illustrated arrangement, reciprocating motion of the upper shoe 29 causes similar reciprocating movement of the grain pan 16. Motion of the grain pan 16 back and forth however is antiphase to that of the upper shoe 29. Thus when the upper shoe 29 is moving forwardly the grain pan 16 is moving rearwardly, and vice versa.
A lower shoe drive link 42 extends downwardly from the underside of the rear of upper shoe 29 and is connected at its lower end to a lower shoe 41 supporting the lower sieve 19, clean grain sheet 21, and tailings sheet 23 beneath the upper shoe 29.
The lower shoe drive link 42 is rigid, is pivotably secured at either end and is further contained by a pivoting yoke 42a mid-way along its length, in a similar manner to link 32. A freely moveable suspension link 39 is pivotably secured at either end near the end of the upper and lower shoes 29, 41 that lies remote from drive link 42. As a result of this arrangement reciprocal back and forth movement of the upper shoe 29 is converted to antiphase back and forth movement of the lower shoe 41 beneath.
The lower shoe 41 supports the lower sieve 19, the clean grain sheet 21, and the tailings sheet 23. Movement of the lower shoe 41 therefore causes movement of these components in a manner that is antiphase to the movement of the parts supported by upper shoe 29.
The frequency of reciprocation of the grain pan 16, the pre-sieve 17, the upper sieve 18, the lower sieve 19, the clean grain sheet 21, and the tailings sheet 23 is the same by reason of the 1:1 transmission ratio represented by the various linkages described.
As a result of this arrangement grains falling onto the grain pan 16 is shaken firstly onto the pre-sieve 17 and thence onto the upper sieve 18. In the illustrated arrangement grains can also fall directly from pre-sieve 17 onto lower sieve 19.
Generally, however, grains sieved by the upper sieve 18 fall onto the lower sieve 19. Crop parts (i.e. incompletely threshed ears, etc.) that do not pass through the upper sieve are moved by reason of its reciprocating motion towards the rear of the upper sieve 18, from where they fall onto the tailings sheet 23 and are returned to the threshing section 11 as described. Lightweight husks and dust as mentioned are blown away from the sieves by the fan 26.
A similar process ensues in relation to the lower sieve 19, with the reciprocating motion causing clean grains to pass through the lower sieve 19 onto the clean grain sheet 21, and causing larger crop plant parts to move to the rear of the lower sieve from where they fall onto the tailings sheet 23.
The reciprocating motions and the angles of inclination of the clean grain sheet 21 and tailings sheet 23 are such as to cause movement of grains or crop parts (as appropriate) thereon along the respective sheets in the directions described above.
Variations on the above-described arrangement are known. It is a characteristic of most if not all of them that multiple sieves and grain or tailings sheets 21, 23 are caused to move in a reciprocal manner as explained.
During the somewhat complex cleaning process described above some grains and ears fall off the lateral edges of the grain sheet 21 and the tailings sheet 23. These would be wasted in the absence of measures to capture them, and to this end flexible (e.g. canvas) seals are installed in conventional combine harvesters 10 along the upper shoe 29 and lower shoe 41. These seals, however, can be relatively ineffective and are prone to failure through wear.
In conventional combine harvesters the clean grain and tailings sheets 21, 23, as explained, are also fixed to the lower shoe 41 which holds the lower sieve 19, such that they are powered by the same mechanism. The clean grain and tailings sheets 21, 23 are inclined when the combine harvester 10 is on level ground, with the result that shaking of the sheets 21, 23 causes movement of the grains in a direction determined by the direction of inclination.
The energy required to move the sieves 17-19 and the clean grain and tailings sheets 21, 23 is high. Apart from a high energy input requirement, the fatigue lives of these parts can be poor. Furthermore as noted despite the attempts made in the grain cleaner to avoid the spillage of grains some grain loss at the sides of the shoes occurs. This reduces the yield of crop, and is undesirable as a result.
It would be desirable to eliminate or at least ameliorate one or more drawbacks of conventional grain cleaners.